1. Field of the Invention
The present invention relates to a continuous casting method and, more specifically, to a technique for continuously casting a bloom or billet.
2. Description of the Related Arts
As this type of technologies, each of Japanese Patent Laid-Open Nos. 2003-305542 and 2002-35896 discloses a casting mold having different tapers.
Japanese Patent Laid-Open No. 2003-305542 describes that since adaptation of a mold to multistage-tapered shape leads to the consumption of mold powder and the resulting sufficient exhibition of lubricating function of the powder, breakout (hereinafter referred also to as BO for short) or bloom cracking can be prevented.
Japanese Patent Laid-Open No. 2004-35896 discloses application of a multistage-tapered mold to casting of so-called billet.
Japanese Patent Laid-Open Nos. 2004-98092 and 2000-158106 disclose techniques related to mold powder.
Japanese Patent Laid-Open No. 2004-98092 relates to a continuous casting method of hyper-peritectic medium carbon steel. According to this document, breakout of constraint (seizure of solidified shell to mold), which tends to occur in low-speed casting of this carbon steel, can be prevented by appropriately setting the chemical composition or physical properties of mold powder.
Japanese Patent Laid-Open No. 2000-158106 also discloses a suitable chemical composition of mold powder similarly to the above-mentioned Japanese Patent Laid-Open No. 2004-98092, wherein main components of this mold powder are regulated to CaO, SiO2 and Al2O3, and the basicity thereof is also mentioned.
However, each of the documents described above independently just devised a countermeasure, paying attention to a specified one of a plurality of factors which deteriorate the surface quality of bloom, and no comprehensive measures have been taken under the present circumstances.